1. Field of the Invention
The present invention relates generally to an apparatus for estimating bit error rate (BER). More particularly, the present invention is directed to a sampling circuit for estimating BER in a wavelength division multiplexing (WDM) communication system.
2. Technical Background
The performance of optical communication systems is generally determined by the bandwidth or data rate of information that can be carried by the communication system. As higher bandwidth optical fibers are developed and higher bandwidth optical communication systems are implemented, it becomes increasingly important to measure the bit error rate (BER) of the signals carried by the optical fiber or communication system. Wavelength division multiplexing (WDM) is one technique for increasing the bandwidth of an optical communication system.
Wavelength division multiplexing (WDM) is the practice of transmitting data streams at multiple wavelengths along a single optical fiber in order to increase the total rate of data transmission along that fiber. WDM also offers the possibility to preform operations upon each wavelength individually. These operations might include adding each wavelength to, or dropping each wavelength from the main data stream, or changing the particular wavelength's intensity or other properties, at locations intermediate to its point of origin and its point of termination. At present, the number of wavelengths used in optical communication systems is increasing, and the number and complexity of different operations performed on the signal, which may effect one or more signals differently than the others is also increasing. This motivates efforts to develop devices for optical monitoring of individual signal wavelengths.
Determining the bit error rate in a wavelength division multiplexing (WDM) channel in an optical fiber is essential for determining and maintaining the health of a WDM communication network. This capability for monitoring the system would ideally, measure channel capacity or bit error rate in a digital communication system independent of the type of modulation present through the channel. In an effort to determine BER in a WDM channel, it is desirable to employ low speed sampling for determining the statistics and/or histogram of the transmitted signals. It is further desirable to implement a sampling technique which offers independence from the transmitted format of the signal, and which can be implemented at low cost.